Vibrational analysis ofp-tert-butyl-calix[4]arene conformers byab initiocalculations

Amiri, Ali; Babaeie, Farzaneh; Monajjemi, Majid

doi:10.1080/00319100701344610

Cited by 6 publications

(4 citation statements)

References 26 publications

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“…All observed bands of TBC[4] are in good agreement with the literature. − The spectrum of free calixarene has a distinctive low-frequency feature at 3123 cm –1 because of stretching of the −OH groups of the cyclic tetramers (Figure ). This stretching arises from the intense intramolecular hydrogen bonding in calixarene that forms an array of circular hydrogen bonding. , The broad band at 1428 cm –1 corresponds to the bending vibrations of −CH2– and the vibrations of aromatic −CC–H .…”

Section: Resultssupporting

confidence: 84%

Novel (Co-,Ni)-p-tert-Butylcalix[4]arenes as Dispersed Catalysts for Heavy Oil Upgrading: Synthesis, Characterization, and Performance Evaluation

Al‐Attas¹,

Zahir²,

Ali³

et al. 2018

Energy Fuels

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This study investigates the promotional effects of a potentially new class of oil-soluble dispersed catalyst precursors for upgrading of vacuum gas oil (VGO), that is metal-based p-tert-butylcalix[4]arenes (TBC[4]s). Co- and Ni-TBC[4] were synthesized, and the metal–ligand complexation was confirmed by scanning electron microscopy-energy dispersive X-ray, inductively coupled plasma, X-ray diffraction, UV–vis, Fourier transform infrared, and 1H NMR. The thermogravimetric and calorimetric behaviors of the synthesized complexes, which are key properties of dispersed hydrocracking catalysts, were also studied. The differential scanning calorimetry profile of Ni-TBC[4] and Co-TBC[4] showed that the organometallic structure has lower thermal stability compared with that of the parent TBC[4]. This apparent drawback can be positively exploited by employing TBC[4] as a carrier of the metal, where the active sites are formed in situ by the destruction of the organometallic complex on reaching the desired reaction conditions. The catalytic performance of the synthesized precursors was evaluated using a batch autoclave reactor with varying concentrations of catalyst precursors at 420–450 °C. The results show that the synthesized metal-based TBC[4] dispersed catalysts evidently enhanced the hydrogenation activity and reduced coke formation. The addition of 500 ppm Co and Ni as standalone dispersed catalysts produced distillate yields of 45.7 and 49.7 wt % and a coke laydown of 2.6 and 2.3 wt %, respectively. Increasing the concentration of catalyst precursors enhanced the conversion of VGO from 86.17% at 100 ppm Ni to 88.28% at 500 ppm Ni. Moreover, as the metal concentration increased from 100 to 500 ppm, the distillate yield increased from 36.87 to 49.66 wt %, while the yield of gases decreased from 20.48 to 17.12 wt % because the hydrogenation reactions were enhanced. In contrast, the yields of distillate and naphtha decreased by 14.12 and 15.36%, respectively, as the temperature increased from 420 to 450 °C.

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Section: Resultssupporting

confidence: 84%

Novel (Co-,Ni)-p-tert-Butylcalix[4]arenes as Dispersed Catalysts for Heavy Oil Upgrading: Synthesis, Characterization, and Performance Evaluation

Al‐Attas¹,

Zahir²,

Ali³

et al. 2018

Energy Fuels

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“…The C–O stretching (1247 cm –1 ) in CX[4] appears at the lower wavenumber than that in CX[5] (1487 cm –1 ). The vibrations due to C–O (1243 cm –1 ) and CC (1606 cm –1 ) stretchings invoking coupling from other internal coordinates as well, in CX[4]- t -Bu compare well with those in the experimental spectra …”

Section: Resultssupporting

confidence: 62%

“…The vibrations due to CÀO (1243 cm À1 ) and CdC (1606 cm À1 ) stretchings invoking coupling from other internal coordinates as well, in CX [4]-t-Bu compare well with those in the experimental spectra. 88 Selected normal vibration frequencies of S-CX[n] derivatives are given in Table 6. As may readily be noticed O1ÀH1 stretching in S-CX [4] predicted at the higher wavenumber (3411 cm À1 ) than CX [4].…”

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confidence: 99%

Electronic Structure, Molecular Electrostatic Potentials, Vibrational Spectra in Substituted Calix[n]arenes (n= 4, 5) from Density Functional Theory

2011

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Electronic structure, molecular electrostatic potential, and vibrational frequencies of para-substituted calix[n]arene CX[n]-R (n = 4, 5; R = H, NH(2), t-Bu, CH(2)Cl, SO(3)H, NO(2)) and their thia analogs (S-CX[n]-R; with R = H and t-Bu) in which sulfur bridges two aromatic rings of CX[n] have been derived from the density functional theory. A rotation around CH(2) groups connecting the phenol rings engenders four, namely, cone, partial cone, 1,2-alternate, and 1,3-alternate CX[n]-R conformers. Of these, the cone conformer comprising of large number of O1-H1···O1' interactions turns out to be of lowest energy. Normal vibration analysis reveal the O1-H1 stretching frequency of unsubstituted CX[n] shifts to higher wavenumber (blue shift) on substitution of electron-withdrawing (NO(2) or SO(3)H) groups, while electron-donating substituents (NH(2), t-Bu) engender a shift of O1-H1 vibration in the opposite direction (red shift). The direction of frequency shifts have been analyzed using natural bond orbital analysis and molecular electrostatic potential (MESP) topography. Furthermore, calculated (1)H NMR chemical shift (δ(H)) in modified CX[n] hosts follow the order: H1 > H3/H5 > H7(a) > H7(b). The δ(H) values in CX[4] are in consonant with the observed (1)H NMR spectra.

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“…Furthermore, large cooperative contributions in CX[4] derivatives are evident from the lower O–H frequencies (by ∼70 cm –1 ) compared to those in CX[5]. Infrared spectral measurements , reveal higher O–H stretching frequencies for thia-CX[4] derivatives compared to those of their unsubstituted analogues. A frequency shift in S-CX[ n ] can be explained on parallel lines, which has partly been attributed to electron density transfer from the bridging sulfur to the benzene ring …”

Section: Resultsmentioning

confidence: 99%

Hydrogen Bond Energies and Cooperativity in Substituted Calix[n]arenes (n= 4, 5)

et al. 2012

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Hydrogen-bonded interactions in para-substituted calix[n]arenes (CX[n]) (n = 4, 5) and their thia analogues are analyzed using the recently proposed molecular tailoring approach. The cooperative contribution toward the hydrogen-bonding network within the CX[5] host is shown to be nearly 5 times larger than that in its thia analogue. Hydrogen bond strengths in the O-H···O network are enhanced on substitution of an electron-donating group. The cooperativity contributions are reflected in the electron density at the bond critical point in the quantum theory of atoms in molecules.

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Vibrational analysis ofp-tert-butyl-calix[4]arene conformers byab initiocalculations

Cited by 6 publications

References 26 publications

Novel (Co-,Ni)-p-tert-Butylcalix[4]arenes as Dispersed Catalysts for Heavy Oil Upgrading: Synthesis, Characterization, and Performance Evaluation

Novel (Co-,Ni)-p-tert-Butylcalix[4]arenes as Dispersed Catalysts for Heavy Oil Upgrading: Synthesis, Characterization, and Performance Evaluation

Electronic Structure, Molecular Electrostatic Potentials, Vibrational Spectra in Substituted Calix[n]arenes (n= 4, 5) from Density Functional Theory

Hydrogen Bond Energies and Cooperativity in Substituted Calix[n]arenes (n= 4, 5)

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